Syphilis, caused by the spirochete bacterium Treponema pallidum subsp. pallidum, is a chronic bacterial infection that remains a public health concern worldwide. Although the majority of the cases occur in developing nations, within the last several years a rapid increase in the number of cases occurring in eastern Europe has been observed, and recent outbreaks have been reported among men who have sex with men in cities across Europe and North America. Further, infectious syphilis directly impacts human health through two additional routes;congenital syphilis continues to be an important pediatric health concern worldwide, and syphilis infection leads to an increased risk of transmission and acquisition of the human immunodeficiency virus (HIV). Interaction of T. pallidum with host cells and tissues is crucial to the infection process, yet little is known about the pathogenic mechanisms used by this pathogen to initiate and establish infection. Treponema pallidum is a highly invasive pathogen;following attachment to host cells, the organism invades the tissue barrier and enters the circulatory system, resulting in widespread bacterial dissemination. One feature crucial to disseminating pathogens is the capacity to attach to the extracellular matrix (ECM) component laminin. This proposal focuses upon the T. pallidum laminin-binding adhesin Tp0751 identified during the previous funding period, and specifically investigates its contribution to the treponemal infection process. In this proposal, the carbohydrate residues on the laminin molecule mediating attachment of Tp0751 will be identified via screening of carbohydrate microarrays. This information will allow for a detailed understanding of the Tp0751-laminin interaction and for determination of the significance of this interaction to pathogenesis. The proposal will also focus upon the co-transcribed open reading frame located upstream of Tp0751, Tp0750. Tp0750 is hypothesized to work in concert with Tp0751 to facilitate invasion and dissemination of T. pallidum, and this proposed role will be investigated herein. Homologs of these proteins are found in two related treponemes, and experiments are proposed to utilize a culturable treponeme as a model system to study the role of these proteins in treponemal pathogenesis. Further, the contribution of these proteins to bacterial metastasis will be determined via in vitro and in vivo dissemination inhibition experiments. The long-term objective of the studies contained in this proposal is to expand our knowledge of T. pallidum pathogenesis by providing a detailed study of the key molecules involved in dissemination of this bacterium. An enhanced understanding of the T. pallidum infection process will allow for the development of novel reagents to combat syphilis infection. Advances made in this field of study will significantly impact public health, both directly through prevention of sexually- and congenitally-transmitted syphilis infections, and indirectly through a concurrent reduction in the acquisition and transmission of HIV.